Food prices will more than double and the number of malnourished children spiral if climate change is not checked and developing countries are not helped to adapt their farming, food and water experts warned on Tuesday at the UN climate talks in Doha.

As the UK energy secretary, Ed Davey, and ministers from 194 countries arrived for the high-level segment of the talks, the UN's Committee on World Food Security said the world would need a 75-90% increase in food production to feed the extra 2 billion people expected to be alive in 2050. But climate change could reduce yields worldwide by 5-25% over the same period.

"The poor are especially vulnerable. Climate change will increase the number of malnourished children substantially. Smallholder farmers will be particularly hard hit," said Gerald Nelson, a spokesman for the high-level panel of experts convened by the committee to report on food prospects in the coming 30 years.

Research from Oxfam suggests rice, maize and wheat prices could rise by up to 177% in the next 20 years if climate change is not checked. A combination of extreme events like the drought that affected North America this year and the Russian heatwave in 2008 could raise prices further than two decades of long-term prices, it said.

"Extreme weather means extreme prices. Our failure to slash emissions presents a future of greater food price volatility with severe consequences for the precarious lives of the people in poverty," said Tracy Carty of Oxfam. "If developing countries are left alone to deal with the impacts of climate change, we are going to see millions of people lose their lands and livelihoods. Investing in the resilience of the poorest communities is not just a matter of justice, but a smart investment in a better collective future on this small planet."

"What we are seeing already in northern Kenya and parts of Africa is food prices skyrocketing as farmers' production declines in successive droughts," said Mohamed Adow, climate adviser to Christian Aid. "The number of people is growing, putting extra stress on food production."

Frustration has grown at the Doha conference over the lack of money being offered by rich countries to help farmers adapt to a world likely to see more extreme weather and events that devastate farming. Wealthy nations have broadly emphasised the need for farming to reduce its emissions using new technologies and carbon markets, while developing countries have wanted more emphasis on help for farmers to adapt.

"African negotiators are throwing their hands up in despair, and asking why they should even bother coming to the negotiations. Their cynicism is at its most stark in the agriculture negotiations," said Seyni Nafo, spokesman for the African group in the talks.

"Many of the solutions to climate change in the dry areas are known," said Mahmoud Solh, Icarda's director general. "They range from water and land management practices to improved crop varieties, and strategies for diversifying traditional crops. The best technologies serve little purpose without a strong policy environment in which they can be put into action, financed and managed."

Bolivia and other Latin American countries with strong indigenous people movements accused rich countries of trying to "commodify" nature by encouraging carbon markets in the same way as forests with the UN's Redd (Reducing Emissions from Deforestation and Forest Degradation) schemes. "It is an attack on nature and common sense that is pushing countries to commodify agriculture with carbon credits as it did with the forests through Redd+, as it intends to do with the oceans and the Earth. Agriculture provides food, give us jobs, gives us life, is the cultural, economic and social basis of our communities, our villages, our producers," said Rene Orellane, head of the Bolivian delegation at the talks. He was backed by India, Argentina, Brazil, Uruguay, Nicaragua, Venezuela and Cuba.

"Carbon markets for agriculture could increase income and reduce emissions. Smallholder farmers can group together to reduce emissions and have a stable income," said Nelson.

But the market approach runs counter to the spiritual beliefs of indigenous peoples. "We have a growing feeling that markets are not the answer. We do not want to put a price on nature. The conference is taking developing countries further and further down the road of markets and away from practical help," said Ariel Chavez, a spokesman for the Latin American regional office of Swedish NGO Diakonia. "We are only hearing about market mechanisms in the conference. But we know that markets are volatile and risky."